1. Field of the Invention
The present invention relates to a process for producing molybdenum oxysulfide dithiocarbamate (hereinafter referred to as MoDTC) and a lubricant composition containing the MoDTC produced by said production process. More specifically, the present invention relates to a process for producing MoDTC which exhibits low corrosive action and has excellent lubricating properties, efficiently in high yields, and a lubricant composition containing said MoDTC.
2. Description of the Related Art
Currently, as automobiles have increased in performance and become high-powered, the conditions of use for engine oils have become more and more severe. Particularly since the reduction of fuel consumption has been gaining attention as an important environmental matter, engine oil viscosity has been reduced, large amounts of friction modifiers have been used, or the quality of friction modifiers have been improved, in order to enhance fuel consumption.
Under such conditions, the use of MoDTC showing excellent friction modifier properties and anti-wear characteristics has become a focus of attention.
Japanese Patent Publication No. 45-24562 discloses a method in which a compound represented by the following general formula: EQU [R.sub.2 N--CS--S].sub.2 Mo.sub.2 (O).sub.m (S).sub.n
(wherein m+n=4, m=2.35-3, n=1.65-1, and R represents a hydrocarbyl group having 1 to 24 carbon atoms) can be obtained from a secondary amine, carbon disulfide and molybdenum trioxide.
Also, Japanese Patent Laid-Open No. 48-56202 discloses a method in which a compound represented by the following general formula: ##STR1## (wherein R is an alkyl group) can be produced by reacting the product given by the method of Japanese Patent Publication No. 45-24562 described above with phosphorus pentasuIfide.
However, the compound disclosed in the above-mentioned Japanese Patent Publication No. 45-24562 shows inferior heat resistance and the compound disclosed in the above-mentioned Japanese Patent Laid-Open No. 48-56202 is corrosive to copper plates, thus the use of those compounds has been limited.
In order to improve such drawbacks, Japanese Patent Laid-Open Nos. 52-19629 and 52-106824 disclose methods to produce a compound represented by the following general formula: ##STR2## (wherein R.sup.5 and R.sup.6 are independently hydrocarbyl groups having 1 to 24 carbon atoms, p is a number from 0.5 to 2.3, t is a number from 3.5 to 1.7 and p+t=4) by reacting carbon disulfide with a secondary amine in an aqueous solution or suspension containing molybdenum trioxide or an alkali metal salt or an ammonium salt of molybdic acid and an alkali hydrogensulfide or an alkali sulfide in a molar ratio of 1:0.05-4.
Also Japanese Patent Laid-Open No. 4-182494 discloses a method by which a compound represented by the following general formula: ##STR3## (wherein R.sup.5 and R.sup.6 are independently hydrocarbyl groups having 1 to 24 carbon atoms, v is a number from 0.5 to 2.3, y is a number from 3.5 to 1.7, and v+y=4) can be produced by reacting carbon disulfide and a secondary amine with an aqueous solution having pH of 8.5 -11, wherein molybdenum trioxide, or an alkali metal salt or an ammonium salt of molybdic acid, and an alkali hydrogensulfide or an alkali sulfide are blended.
The methods disclosed in the above-mentioned Japanese Patent Laid-Open No. 52-19629, Japanese Patent Laid-Open No. 52-106824, and Japanese Patent Laid-Open No. 4-182494, are for obtaining MoDTC which has nearly the same skeletal structure as the end-product, by using a hexavalent molybdenum compound as a starting material. However, the yields remain low, and the purity of the product is low as well, thus the product has poor lubricity.